1. Field of the Invention
The present invention is directed to processing sequences, refining sequences, and power-generation industries that employ separation devices in which non-vapors and vapors are to be separated. More particularly, the present invention is directed to cyclone/vortex methods for the separation of non-vapor and vapor components in distillation/flashing processes, and processes that benefit from a reduction of entrainment of liquids and solids in the vapor. Still further, the present invention is directed to processes for the reduction of catalyst loss during the separation of non-vapors and vapors.
2. Description of Related Art
In many distillation/flashing processes with mixed phase feed, entrainment of liquid droplets in the vapor rising from the feed zone is undesirable in terms of both economics and product purity. Problems concerning the entrainment of liquid materials in vacuum flasher units are well recognized in the art as represented by U.S. Pat. No. 5,743,926 to Bannon et al. As noted in Bannon et al., trays may be placed directly above the feed zone to remove entrained droplets from vapor in hydrocarbon processing and refining. Bannon et al. further note that a disentrainment or wash-oil section may be incorporated in refineries to reduce entrainment problems by knocking liquid droplets out of a vapor stream as it proceeds to the vapor outlet of a vacuum flasher. Despite the methods claimed by Bannon et al., however, methods for reducing entrainment that are both effective and efficient from a costs stand-point remain lacking in industry.
Another problem in terms of both economics and product purity is the entrainment in the vapor overhead of dissolved or suspended solids, such as catalyst(s). Entrained solids can be detrimental to product purity, or can foul downstream equipment. In addition, entrained solids can translate into a loss of a valuable chemical, such as a catalyst. In this regard, U.S. Pat. No. 6,153,792 to Leet et al. discloses a process for the production of a carboxylic acid in the presence of solid catalyst particles that employs a flash step, using trays and a liquid wash. The liquid wash step disclosed by Leet et al. generally xe2x80x9cwashesxe2x80x9d attrited catalyst particles in upward flowing vapors, downward in the flasher. U.S. Pat. No. 4,247,486 to Brewster et al. and U.S. Pat. No. 4,287,369 to Harris et al. mention the loss of rhodium catalyst by entrainment in reactor overhead, and disclose the use of demisting pads to remove entrained liquid droplets for return to the reactor. Despite the methods claimed by Leet et al., Brewster et al., and Harris et al., methods for reducing entrainment of dissolved or suspended solids and loss of valuable chemicals such as catalysts that are both effective and efficient from a costs stand-point remain lacking in industry.
Reducing the amount of catalyst lost through entrainment has been a concern in a wide variety of industries, as represented by U.S. Pat. No. 4,166,773 to Higley et al.; U.S. Pat. No. 4,163,701 to Strong; and U.S. Pat. No. 4,871,879 to Laird. None of these methods, however, have fulfilled the needs in industry.
The method of the present invention fulfills multiple needs in industry: (1) a reduction of entrainment of liquids, and dissolved or suspended solids, in a separated vapor; (2) a reduction in the amount of valuable chemicals lost, as a result of the reduction of entrainment; (3) making it possible to use a smaller and less expensive separation vessel to reduce entrainment where before only a larger and more expensive vessel could be used for the same purpose; and (4) making it possible to retrofit existing separation vessels so as to achieve the reduction in entrainment without the need to build an entirely new vessel.
According to the present invention, methods are provided for reducing entrainment of solids and liquids, collectively referred to as xe2x80x9cnon-vaporxe2x80x9d, in a vapor flow exiting a separation vessel. According to preferred methods of the present invention, one or more of the following steps may be performed to reduce the entrainment of non-vapor in a vapor flow exiting a separation vessel: (1) minimizing the climbing or creeping of the stream toward the vapor outlet along the inner surface of the separation vessel from the point of introduction of the stream; (2) reducing the amount of non-vapor, if any, that exits from the separation vessel through the vapor outlet; and (3) maximizing the flow of the stream tangentially to the inner surface of the separation vessel, hereinafter referred to as xe2x80x9ctangential coherency.xe2x80x9d
The methods of the invention comprise introducing a stream into a separation vessel having an inner surface, at least one inlet, and at least one vapor outlet. The stream can be any mixture of vapor and non-vapor. The term xe2x80x9cvaporxe2x80x9d as used herein shall mean vapor and/or gas. The term xe2x80x9cnon-vaporxe2x80x9d as used herein shall mean liquids, solids such as catalysts, and mixtures of liquids and solids, including solutions and suspensions. According to the methods of the invention, the stream contains at least one non-vapor and at least one vapor. The stream is introduced to the separation vessel through the inlet(s), where the velocity of the stream is reduced upon introduction into the separation vessel, and where the tangential coherency of the stream is maximized. Reducing the velocity of the incoming stream and maximizing its tangential coherency contributes to the minimization of the tendency of the stream to move along the inner surface of the separation vessel toward the vapor outlet and contributes to a reduction in entrainment.
According to the method of the present invention, a vapor flow is separated from the stream in the separation vessel, and rises within the separation vessel at non-uniform vapor velocities. The vapor flow exits the separation vessel through the vapor outlet(s), moving at vapor flow exit velocities. According to a preferred embodiment of the present invention, the non-uniform velocities at which the vapor flow flows within the separation vessel may be distributed to aid in reduction of entrainment of non-vapor and loss of valuable non-vapor components such as catalysts. The distribution of vapor velocities contributes to a reduction in the tendency of the stream to move along the inner surface of the separation vessel toward the vapor outlet, and also minimizes the vortex capabilities of the rising vapor flow, thereby reducing entrainment of non-vapor.
According to further preferred embodiments of the present invention, the stream is guided along a path when it is introduced to the separation vessel such that tangential coherency is maximized, such that the tendency of the stream to move along the inner surface of the separation vessel toward the vapor outlet is minimized, and such that the amount of non-vapor that exits with the vapor flow through the vapor outlet(s) is minimized.
Still further preferred embodiments of the present invention for reducing entrainment of non-vapor and loss of valuable non-vapor include controlling the vapor flow exit velocities such that the tangential coherency of the stream is maintained, such that the tendency of the stream to move along the inner surface of the separation vessel toward the vapor outlet is minimized, and such that the amount of non-vapor that exits the separation vessel with the vapor flow through the vapor outlet(s) is minimized.
According to still further preferred embodiments of the present invention, a cyclone, as known in the industry, can also be used in combination with other embodiments of the present invention to recover any of the non-vapor that exits the separation vessel with the vapor flow.
The methods of the present invention are more fully explained in the following detailed discussion and examples.